APPARATUS, METHOD AND COVERING DIE FOR PRODUCING A LONG FIBER-REINFORCED THERMOPLASTIC COMPOSITION

Abstract: An apparatus, a method and a covering die for producing a long fiber-reinforced thermoplastic composition for reducing unevenness in extrusion in a web width direction when covering a bundle of continuous fibers which are opened in a web form with fused thermoplastic resin extruded from a slit, wherein fused thermoplastic resin is extruded from a slit set so as to have a width substantially equal to that of the web and a gap changing in the web width direction to thereby cover at least one side of the moving bundle of continuous fibers which are opened in a web form.

Description: The present invention relates to an apparatus and a method for producing a long fiber-reinforced thermoplastic resin composition composed of a thermoplastic resin and fiber bundles. The invention also relates to a die used in the production of composite materials of a thermoplastic resin and fiber bundles, and more particularly, to a coating die used in the production of a long fiber-reinforced thermoplastic resin composition. US patent 3956056 relates to a method and apparatus for coating a cord fabric with elastomeric stock to achieve improved impregnation of the fabric. The fabric is fed by a driven roller which is confronted by a stationary dieblade and defines therewith a convergent nozzle-like chamber. The chamber is elongated in the direction of advancement of the elastomer so as to resist swelling of the elastomer as it issues with the fabric. As examples of apparatus for producing long fiber-reinforced thermoplastic resin compositions, there are coating dies with interior passages. Fiber bundles in the form of a web are passed continuously through the interior passages, while a thermoplastic resin melt is extruded into the passages for coating the fiber bundles. The resin coat is allowed to permeate into the fiber bundles. Japanese Patent Application Laid-open (kokai) No.63-264326 discloses a coating die used in the production of thermoplastic resin profiles reinforced with continuous long fibers. Continuous roving fibers are coated with a thermoplastic resin inside the die. Fig. 7 in the present specification is an example of the die used for coating described in that publication. A thermoplastic resin supplied from an extruder to supply tubes 2 and 2' as indicated by arrows F 1 and F 2 is allowed to pass through slits S 1 and S 2 which are elongated in the width direction W for permeating into and coating a roving which moves through an interior passage in the direction of arrow H. The coating die disclosed in Japanese Patent Application Laid-open (kokai) No 63-264326 has the drawback that supply of a resin melt, coating of fiber bundles, and impregnation of fiber bundles tend to become uneven in the width direction of the roving. Moreover, differences in supply pressure and in amount of supply of the resin which is supplied in the width direction of the roving brings about further problems of clogging of the die and breakage of fibers which occurs due to the uneven shear force against the resin generated inside the subsequent forming die. The present invention was accomplished after careful studies in view of the above problems. It is therefore an object of the present invention to solve the above problems and to provide an apparatus, a method, and a coating die for producing a long fiber-reinforced thermoplastic resin composition. Accordingly, the present invention is drawn to a coating die for producing a long fiber-reinforced thermoplastic resin composition in which at least one of the upper and lower sides of a fibrous web which has undergone fiber-loosening and which passes through the die is coated with a thermoplastic resin melt supplied from an extruder through a resin supply path, said die including an extrusion slit having substantially the same width as that of the web, characterized in that the slit has a spacing which changes across the width of the web so as to have an increased spacing as it becomes more remote from the extruder. The term "fibrous web" as used herein refers to a web-like continuous bundle of fibers to be passed through the die. The present invention also provides a method for producing a long fiber-reinforced thermoplastic resin composition in which at least one of the upper and lower sides of a fibrous web which has undergone fiber-loosening and which passes through the die is coated with a thermoplastic resin melt which is extruded through a slit having substantially the same width as that of the web, characterized in that the slit has a spacing which changes across the width of the web so as to have an increased spacing as it becomes more remote from the extruder. Another aspect of the present invention is drawn to a coating die for producing a long fiber-reinforced thermoplastic resin composition as described above, wherein the spacing of the slit is tapered. The invention also encompasses an embodiment in which the spacing of the slit is changed by the use of retractable block pieces. In one aspect of this embodiment the retractable block pieces are positioned to change the configuration of the slit at its port so as to vary the amount of supply of the thermoplastic resin melt in the width direction of the web. In a further aspect of the said embodiment, the retractable block pieces change the spacing of a supply part of the slit in the die, again so as to vary the amount of supply of the thermoplastic resin melt in the width direction of the web. A further aspect of the present invention is drawn to a coating die as described above, characterized in that the slit is formed between a stationary slit-forming member and a movable slit-forming member which is pivotable about a hinge provided at one end thereof. The expression "one end of a slit-forming member" is intended to mean an end portion or its vicinity of a slit-forming member. In the above-described aspects of the present invention, the width of the slit may be slightly different from that of the web so long as the two widths are approximately identical. Hereafter, a description will be given centering on a typical coating die for producing long fiber-reinforced thermoplastic resin compositions of each aspect. With the coating die for producing long fiber-reinforced thermoplastic resin compositions of the present invention, it is possible to sequentially or arbitrarily change, in the width direction of the web, the amount of a thermoplastic resin extruded. Due to the positional relationship and the like of the slit and the supply path of a thermoplastic resin melt supplied from outside the coating die by an extruder, etc., conventional slits having a constant spacing cannot avoid uneven extrusion of a thermoplastic resin melt in the width direction of a web since the supply pressure of the resin applied to the portion of a slit on the upstream side of the supply path is greater than that applied to other portions of the slit. According to the coating die of the present invention, it is possible to eventually achieve uniform extrusion. When a slit having a constant spacing in the width direction of the web of a continuous fiber bundle is used, the spacing of a narrow part of the resin path in the die leading to the slit is reduced by the use of retractable block pieces of the present invention so as to change the amount of supply of a resin melt in the width direction of a web. Therefore, in a case where the spacing of the narrow part of the resin path is not reduced and the amount of extrusion from the slit is uneven in the width direction of the web, it is possible to eventually make uniform the amount of the thermoplastic resin extruded. Brief Description of the Drawings: Fig. 1(a) is a plan view showing a die according to an embodiment of the present invention. Fig. 1(b) shows the cross-section of (a) cut along the line AA. Fig. 2 is an illustration directed to a slit according to another embodiment of the present invention. Fig. 3 is an illustration directed to a slit according to a still further embodiment of the present invention. Fig. 4(a) is a plan view of an embodiment in which a narrow part of a path for supplying a thermoplastic resin melt is reduced in the width direction of a web by the use of block pieces. Fig. 4(b) shows the cross-section of (a) cut along the line BB. Fig. 5(a) is the cross-section cut along the line BB which corresponds to the case where  is 0° in Fig. 4(b). Fig. 5(b) is the cross-section cut along the line BB which corresponds to the case where  is 90° in Fig. 4(b). Fig. 6 is a plan view showing an embodiment in which the spacing of a slit is adjusted by a hinge. Fig. 7 is a perspective view showing a conventional coating die according to the prior art described above. Some essential reference numerals are listed below. 2, 20: A path for supplying a thermoplastic resin 3: Slit port 22: Adjustable internal part of the slit W: Width direction of a fibrous web A 1 , A 2 , ... A n : Block pieces B 1 , B 2 , ... B 6 : Block pieces t 1 , t 2 : Spacing of a slit H: A hinge Coating dies for producing a long fiber-reinforced thermoplastic resin composition according to the aspects of the present invention will next be described with reference to the drawings. Fig. 1(a) is a plan view of a slit for extruding a thermoplastic resin according to a first embodiment of the invention, as viewed when the die is cut through an interior passage (as shown in Figure 7) provided for passing a web therethrough in the case where a thermoplastic resin melt for coating a web is supplied from beneath the web. Fig. 1(b) is a cross-section of (a) cut along the line AA. The left hand side of Fig. 1(b) becomes the top of the die. A thermoplastic resin melt is introduced into the die from an extruder 1, passes through a resin supply path 2 provided inside the die, and is extruded through a slit port 3 over the width W of the web. The die has a rough surface 4 over which the web passes in a subsequent impregnation step. In Fig. 1(a), the spacing of the slit port 3 is tapered from the left hand side spacing t 1 to the right hand side spacing t 2 (t 2 > t 1 ). Since the right hand side (slit spacing: t 2 ) of the die is more remote from the extruder 1 than is the left hand side (slit spacing: t 1 ) and as a result undergoes a smaller resin pressure, the spacing of the slit port 3 is increased. With this structure, it is possible to achieve extrusion of a thermoplastic resin with an almost uniform volume across the width W of the web. Therefore, if the die has a structure in which a thermoplastic resin melt is supplied from the left hand side as shown in Fig. 1, in contrast to the previous situation in which shortage of a resin or insufficient extrusion of a resin occurs at the right hand side of a slit to cause uneven extrusion in the width W of the web when the resin is extruded through a slit with a constant spacing, the present embodiment in which the spacing of the slit port 3 at the right hand side t2 is made greater than t 1 at the left hand side can suppress shortage of a resin at the right hand side, obtaining a uniform amount of extrusion across the width W of the web. The values t 1 and t 2 are selected so as to assume a proper ratio in accordance with conditions such as the species of the resin material and the extrusion temperature. Depending on the fluidity behavior of the thermoplastic resin melt, the slit may have a spacing having a certain curved configuration rather than the tapered spacing. Fig. 2 is a schematic illustration of a slit embodiment in which block pieces are used for changing the spacing of a slit port 3 across the width W of a web. The broken line of the slit port 3 shows the case where the spacing of the slit port 3 is constant and not changed in the width direction W of a web. In this Figure 2 embodiment, however, block pieces B 1 to B 6 are adjusted by being retracted or advanced in the direction perpendicular to the direction W and are fixed after their positions are adjusted. In this particular embodiment, the spacing is stepwise varied from t 1 to t 2 in the width direction W so as to widen the spacing of the slit port 3. In cases where the right hand side of the slit is considerably liable to shortage of a thermoplastic resin melt, or where extrusion volume is significantly insufficient, the amount of extrusion can be made uniform by making the distance t 2 greater than t 1 . If a prolonged portion in the width direction of a web represents a satisfactory extrusion (where occurrence of shortage of a resin is suppressed), the width of a block piece L 1 may be made greater than that of another piece, for example greater than L 2 as shown in Fig. 2 so as to vary the spacing of the slit in a stepwise manner. Moreover, if necessary, the spacing of the slit may be varied in a curved manner by modifying the shape of the fore end of the block piece. An embodiment in which the spacing of a slit is varied in the width direction W of a web in a more complicated manner is described while referring to Fig. 3. In contrast to cases shown in Figs. 1 and 2 where the spacing of a slit uniformly increases from the left hand side to the right hand side in the drawings, an embodiment shown in Fig. 3 can achieve the object of the present invention, i.e., make uniform the extrusion volume through a slit if the path 2 for supplying a thermoplastic resin into the die is located at a position which faces the vicinity of the center in the width direction of a web, and the path leading to the slit is branched in the right and left directions. Briefly, at the vicinity of the center of the slit, pressure and temperature of the resin are higher than those at other portions, and accordingly, the fluidity of the resin is high. As this means less risk of occurrence of shortage of resin, the spacing of the slit SC is made relatively small. On the other hand, at the left and right hand sides which are remote from the central supply port, pressure and temperature of the thermoplastic resin melt is reduced so as to decrease the fluidity of the resin melt and to raise the risk of resin shortage, the slit spacings SL and SR are increased. With this structure, it is possible to achieve more uniform extrusion in the width direction W of a web relative to the case where a resin is extruded through a slit with a constant spacing. Another embodiment is described while referring to Figs. 4(a) and 4(b), in which the supply volume of a thermoplastic resin melt is made variable in the width direction of a web by the use of retractable block pieces (A 1 to A n ) to reduce the spacing of part of the resin path leading to the slit port. Fig. 4(a) is a plan view of a slit similar to that shown in Fig. 1. Fig. 4(b) shows the cross-section of Fig, 4(a) cut along the line BB. In Figs. 4(a) and 4(b), a thermoplastic resin melt is introduced through an extruder 10 into the die, passes through a path 20 provided inside the die, and is distributed over the web in its entirety in the width direction W of the web. The resin thus supplied is extruded through a slit port S after passing between a block piece A supported by a bolt 25 and a part 22 of the slit inside the die body between the resin path 20 and the slit port S. Each of the block pieces A 1 to A n is provided with a bolt 25. By adjusting the bolts 25, the block pieces A are each independently retracted or advanced so as to widen or narrow slit portions L 1 to L n corresponding to the block pieces A 1 to A n . By so controlling the spacing of the part 22 of the slit, it is possible to adjust the extrusion volume so as to make it uniform in the width direction W of a web, even though the slit port S has a constant spacing, in accordance with the fluidity behavior of the thermoplastic resin to be used. For example, if the part 22 of the slit portion L 1 is minimized by the use of a block piece A 1 and the position of each block piece A is adjusted by a bolt 25 so that the spacing of the part 22 gradually increases toward the block piece A n , effects similar to those obtainable from the embodiment shown in Fig. 2 can be obtained. The angle of inclination  of the part 22 with respect to the die body is not particularly limited. The angle may be approximately 60° as shown in Fig. 4(b). Alternatively, it may be 0° as shown in Fig. 5(a), or 90° as shown in Fig. 5(b). In both drawings, only an essential portion of a cross section cut along the line BB in Fig. 4(b) is illustrated. Another embodiment will next be described while referring to Fig. 6. In this embodiment, a hinge is used to alter the spacing of a slit in the width direction of a web. In Fig. 6, H indicates a hinge, M indicates a movable slit-forming member, P indicates its fore end, and N indicates a stationary slit-forming member. The movable slit-forming member M is moved, about the hinge H, with respect to the stationary slit-forming member N. The movable slit-forming member M is fixed to its counterpart at a proper position using a bolt Q, etc. This makes it possible to vary the spacing of a slit in a tapered manner in the width direction W of a web over one end with a narrow spacing t 1 to another end with an expanded spacing t 2 . In Fig. 6, a slit-end sealing means is not shown which is required by the movable slit-forming member M. When a continuous fiber bundle in the form of a web is coated with a thermoplastic resin melt, the resin melt may be extruded from above the web or from both the above and beneath the web as shown in Fig. 7, rather than being extruded from beneath the web. Examples of the thermoplastic resin used for applying to a fibrous web for impregnation include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyamides such as nylon 6, nylon 66, nylon 11, nylon 12, nylon 610 and nylon 612; polyacetals, polycarbonates, polyurethanes, polyphenylene sulfides, polyphenylene oxides, polysulfones, polyetherketones, polyetheramides, polyetherimides, other thermoplastic resins, and combinations of these. The molecular weight of these resins is not particularly limited so long as they exhibit proper fiber-reinforcing effects when permeated into the fibers. Various additives may be added to the thermoplastic resins in accordance with the end use of the resin composition and conditions under which the resin composition is used. Such additives include anti-oxidants, antistatics, impregnation accelerators, plasticizers, mold releasing agents, fire retardants, fireproofing aids, crystallizing accelerators, colorants, and fillers. As described above, if the coating die for producing a long fiber-reinforced thermoplastic resin composition of the present invention is used, irrespective of the position at which a thermoplastic resin melt is introduced into a die or of changes in fluidity behavior of the resin melt, it is possible to control and suppress uneven extrusion in the width direction of a web when a thermoplastic resin melt is extruded through a slit having approximately the same width of a continuous fiber bundle in the form of a web. As a result, the invention provides an effect of suppressing the risk of partial shortages or the like of a resin in the width direction of the web compared to the case where a coating die with a constant spacing is used. Moreover, if block pieces are used, finer adjustment can be achieved. In addition, even when part of a block piece is accidentally broken for some reason, exchange of that particular piece makes it ready to use the coating die.

Claims: A coating die for producing a long fiber-reinforced thermoplastic resin composition in which at least one of the upper and lower sides of a fibrous web which has undergone fiber-loosening and which passes through the die is coated with a thermoplastic resin melt supplied from an extruder (1,10) through a resin supply path (2,20), said die including an extrusion slit having substantially the same width as that of the web, characterized in that the slit has a spacing which changes across the width (W) of the web so as to have an increased spacing as it becomes more remote from the extruder (1,10). A coating die as claimed in Claim 1, characterized in that the spacing of the slit is tapered. A coating die as claimed in Claim 1 or claim 2, characterized in that the die includes retractable block pieces (A, B) for changing the spacing of the slit. A coating die as claimed in claim 3, characterized in that the retractable block pieces (B) are positioned to change the configuration of the slit at its port (3) so as to vary the amount of supply of the thermoplastic resin melt in the width (W) direction of the web. A coating die as claimed in claim 3, characterized in that the spacing of a supply part (22) of the slit is changed by retractable block pieces (A) so as to vary the amount of supply of the thermoplastic resin melt in the width (W) direction of the web. A coating die as claimed in claim 1 or claim 2, characterized in that the slit is formed between a stationary slit-forming member (N) and a movable slit forming member (M) which is pivotable about a hinge (H) provided at one end thereof. A method for producing a long fiber-reinforced thermoplastic resin composition in which at least one of the upper and lower sides of a fibrous web which has undergone fiber-loosening and which passes through the die is coated with a thermoplastic resin melt which is extruded through a slit having substantially the same width as that of the web, characterized in that the slit has a spacing which changes across the width (W) of the web so as to have an increased spacing as it becomes more remote from the extruder (1,10). A method as claimed in claim 7, characterized in that the fibrous web is subsequently impregnated by passage over a rough surface (4).

Inventors: AMAIKE TAKESHI, HIRAGOHRI MOTOHITO, MURAKAMI HARUJI, SHIRAI YOSHIMITSU, AMAIKE, TAKESHI, HIRAGOHRI, MOTOHITO, MURAKAMI, HARUJI, SHIRAI, YOSHIMITSU
Applicants: POLYPLASTICS CO, POLYPLASTICS CO. LTD.
Application year: 1994
Main classification: B29C70
IPC codes: B29C47, B29B15, B29C70, B29K105, B29K101